Today I wrote two different Guava Collections as answer to two different StackOverflow Questions:
The first requested a Map where the keys are Enums and the values are sorted collections.
In my answer, I implemented a Guava MultiMap that does just that. It uses EnumMap internally if it knows the enum’s type and a HashMap or a user-supplied map otherwise (each of these three Constructors has a sibling with a custom comparator that sorts the values).
The second was apparently based on the first and dealt with the problem that the OP would like to use a SortedSet, but the business objects did not have a valid compareTo() / equals() relation, so I suggested that a sorted List would be better. I implemented such a List using Guava’s ForwardingList as base and redirecting the logic to an internal ArrayList.